Temperature sensor



Aug- 29, 1967 H. M. LNDIS ETAL. 3,339,164

TEMPERATURE SENSOR Original Filed Oct. 20, 1965 5 Sheets-Sheet i3 U GEDELEMENTS 109 vous APPLIED VOLUME RESlSTlVITY OHM CM PoTAssluM* RATE r lN03 NQUACIING. |A

Aug- 29, l967 H. M. LANDIS ETAL L3,339,164

TEMPERATURE SENSOR original Filed oct. 2o. 1965 5 sheets-sheet :s

10.2 SWAGED ELEMENTS 42 vous APPLIED k-QUARTZ 1o \\+PYREX \f\ :5E- 107 oREPEATABLE\\` BREAK-DOWN REslsTlvlTlEs 6 LIME GLASS K 10 u,

coNoucTlNG TEMPERATURE c Fys.

Aug. 29, 1967 5 Sheets-Sheet riginal Filed Oct. 20, 1965 LOAD Aug 29,1967 H. M. I ANDIS ETAL 3,339,164

TEMPERATURE SENSOR Original Filed Oct. 20. 1965 5 Sheets-Sheet UnitedStates Patent O 3,339,164 TEMPERATURE SENSOR Harry M. Landis, Norton,and Joseph W. Waseleski, Jr.,

Manstield, Mass., assignors to Texas Instruments Incorporated, Dallas,Tex., a corporation of Delaware Original application Oct. 20, 1965, Ser.No. 498,267, now Patent No. 3,295,087. Divided and this application Oct.3, 1966, Ser. No. 583,908

9 Claims. (Cl. 338-22) ABSTRACT F THE DISCLOSURE This applicationdiscloses solid-state NTC sensor products composed of an outer electrodein the form of a shell, inner electrodes in the form of one or more coremembers and particulate material compressed between electrodes. Asolid-phase interatomic bond exists between the surfaces of theelectrodes and the particles lying adjacent thereto and between some butnot all of the particles. The devices are characterized by exhibiting arepeatable, non-catastrophic breakdown of the resistance at a certaintemperature level and the compressed particulate material has aconductivity which is not less than approximately 50% of the theoreticalconductivity of the material from which they are formed. The temperatureresistivity characteristics of the sensors are variable under a variableapplied electric load. The particular embodiments shown include a sensorhaving a solid central core and an outer sheath with a compressedsolidstate sensing material held therebetween. Another embodiment-has acentral hollow tubular core, an outer sheath and compressed sensingmaterial held therebetween while still another embodiment has a centralhollow tubul-ar core with a central rod-like core located within thehollow core and a first compressed sensing material held between thesheath and hollow core and a second compressed sensing material heldbetween the hollow core and the rod-like core. The first and secondcompressed sensing material in the last mentioned embodiment may becomposed of the same or different compositions or compounds. Circuitsare disclosed in which the sensors are employed.

This application is a divisional application of our U.S. patentapplication Ser. No. 498,267, filed Oct. 20, 1965 now Patentl No.3,295,087, for Temperature Sensor and is a contin-uation-in-part of our-U.S. patent application Ser. No, 331,712, tiled Dec. 19, 1963 nowPatent No. 3,266,001, for Temperature Sensors and their Manufacture.

This invention relates to `temperature sens-ors and their manufacture,and with regard to certain more specific features, to 4solid-statesensors of this type having negative temperature coeflicients ofresistance (NTC sensors).

Among the several objects of the invention may be noted the provision oflow-cost means for the fabrication of strong, stable and compactsolid-state NTC sensor products from a variety of starting materials;the provision of such sensors having advantageous physical formssuitable for convenient storage and flexible application andminiaturization in a wide variety of electrical circuits; the provisionof sensors of the class described having resistivities which are afunction of both temperature and electrical field strength (voltage);the provision of sensors of this class including such as will exhibitnoncatastrophic and repeatable so-called breakdown effects in theirtemperature-resistivity functions; the provision of sensors of the classdescribed having uniform critical charactervistics from point to pointin their compositions and which may be operated many times withoutdamage to or appreciable change in such uniform characteristics; .theprovision of improved thermostatic controls employing such sensors; andthe provision of sensors which can be made to produce either a singleoperating signal, or multiple operating signals which may be the same ordifferent. Other objects and features will be in part apparent and inpart pointed out hereinafter.

The invention accordingly comprises the products, devices and methodshereinafter described, the materials and combinations of materials, theproportions thereof, steps and sequence of steps, and features ofconstruction, composition and manipulation which will be exemplified inthe following description, and the scope of the application of whichwill be indicated in the following claims.

In the accompanying drawings, in which several of various possibleembodiments of the invention are illustrated,

FIGS. l and 2 are axial sections of parts in arrangements according tocertain preliminary steps employed in carrying out the invention; p

FIG. 3 is a side elevation illustrating one of repeated reducing stepswhich are applied to the parts as shown in FIG. 2;

FIG. 4 is a view of an elongate intermediate coilable sensor productaccording to the invention, after swaging steps have been completed;

FIG. 5 is a greatly enlarged typical cross section taken on line 5-5 ofFIG. 4;

FIG. 6 is a perspective view of a typical end or sensor made accordingto the invention;

FIGS. 7 and 8 are charts illustrating certain operating characteristicsof certain products made according to the invention;

FIGS. 9 and 10 are schematic circuit diag-r-ams of two exemplaryembodiments of thermostatic control apparatus of the present invention;and

FIGS. 1l-l2 are diagrammatic cross sections of alternative forms of theinvention.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

Sensors of the type herein described may be made from members of severallarge classes of materials, namely:

( l) Inorganic insulators such as A1203, BaTiO3,

C0203, CUO, F6203, V205, STO3, B-aZrO3, KNO3, quartz, glasses steatite,the like;

(2) Inorganic semiconductors such as V204 with Bi, Sb, etc., dopedBaTiO3, Ge, Si, In, and the like;

(3) Crystalline organic insulators such as sucrose, dextrose and thelike.

' The formula for a typical doped BaTiO3 is BalggqLamsTiOa. This mayexhibit PTC characteristics in some temperature ranges.

Typical glasses are lime glasses, Vycor glass, Pyrex Iglass IR(infrared). The words Vycor` and Pyrex are trademark designations of theCorning Glass Works of Corning, New York. A typical IR glass is a glasshaving a composition designated (Si1 X y ZAsXSeyTeZ).

It is knownthat single-crystal or bulk specimens of various materials,including those above mentioned, have certain temperature coelicients ofresistivity, some of which are exclusively negative and some of which,such as for example, lanthanum-doped BaTiO3, exhibit negative (NTC)characteristics only in certain ranges and positive (PTC)characteristics in other ranges. Most of these materials, such as thoseindicated in FIGS. 7 and 8 and later to be more fully described, havebreakdown resistivities at certain temperatures. Such breakdownresistivities are yusually catastrophic in the sense thatthey productNaNOg, PbTiO3, Rochelle Salt and doped Sb, GaAs,

are not repeatable and therefore comparatively useless for the objectsof the invention.

To make a sensor of single-crystal or bulk materials involves tediousand costly fabricating operations which the present invention avoids.Such single crystal or bulk materials have anisotropic properties, whichcannot be put to use unless such bulk crystals or bulk materials areproperly oriented with respect to the appropriate electricalconnections. This has required tedious and costly procedures toaccomplish, such as slow growing or deposition of crystals and costlymethods of connecting circuitry thereto.

By means of the present invention, materials such as above listed arereduced to, and then worked more readily in a finely divided state toproduce sensors. Ordinarily use of finely divided materials would makethe handling of individual particles even more difficult in order totake advantage of their anisotropic properties. By means of theinvention such difficulties are completely removed. In addition,unusually compact and strong sensor materials, and sensors combined withterminal contacts, are obtainable by means of the invention.

Another advantage of the invention is that sensors can be made whichhave resistivity-temperature functions which can be varied by change inthe strength of an applied electrical eld. This is generally usefulwhether or not such materials exhibit the so-called breakdown effect butis particularly useful in the cases of those materials that have suchbreakdown effect. The breakdown effect is one according to which thematerial in the solid state at a certain temperature suddenly decreasesin resistance almost to zero. Whether or not a given material has abreakdown point, its curve of resistivity versus temperature can beshifted by a change in applied voltage. This feature is useful in thefield of thermostatic controls, such as will be explained in connectionwith FIGS. 9 and 10. These show that simple thermostats may be madehaving repeatable voltage-adjustable trip temperatures.

Sensors, thermostats and other apparatus made according to the inventionare cyclically operable many times, even through a breakdown event (whensuch occurs), with no appreciable damage or change in characteristics.

Tentative theories hypothecated herein concerning why the inventionworks are given for explanatory purposes and are subject to possiblechange. It will be understood, however, that the forms and advantages ofthe invention are independent of any theories which might explain them.

Hereinafter the following are to be taken as equivalents:

(A) Shell, sheath, sleeve, jacket or container;

(B) Core, rod or wire;

(C) Powdered, finely divided or particulate material;

(D) Contacts, terminals or connectors;

(E) Swaging, wire drawing, extruding, tubing, rolling or deforming;

(F) Metals and their alloys.

Referring now more particularly to FIGS. 1-5, there is shown at numeral1 a cylindrical container, sleeve or sheath composed of a malleable andelectrically conductive metal. Spacedly centered within the shell 1 is acore 3 which is in the form of a malleable and electrically conductiverod or wire. At numerals 5 and 7 are cylindrical end plugs composed ofany suitable material to effect closure. Members 1, 3, 5 Iand 7 may inlower temperature applications be composed of stainless steel, copper,silver, aluminum, brass or the like, and for higher temperatures morerefractory metals such as nickel, monel, Inconel, molybdenum, tantalumor the like.

As shown in FIG. 1, the end plug 5 has welded or otherwise held withinit one end of the core 3 and is itself welded or otherwise held withinone end of the shell 1. Plug 7 is initially left out of the sleeve 3 asshown. Both plugs 5 and 7 ultimately provide means for enclosing theannular cylindrical space 9 left between the sheath 1 and core 3 and forsubstantially centering the core 3.

Prior to the condition shown in FIG. l, the parts 1, 3, 5 and 7 arecleaned by appropriate conventional pickling in acid baths. Theparticular pickling procedures depend upon the metals of which thesheath and core are composed. Such are known and require no furtherdescription. After pickling, the parts are washed with distilled waterand dried, whereupon they are ready for further manipulations. Cleaningof plugs 5 and 7 is elective because these ultimately become part of aminor amount of end scrap.

Before the plug 7 is inserted between the members 1 and 3, finelydivided clean material 11 is poured as a filling into the space 9, asindicated by the curved darts 13. The finely divided filling mass iscomposed of material such as set forth in lists (l), (2) and (3) above(or the like), which has been crushed from the whole crystal or bulkform to a particle size, preferably below substantially 40 mesh (U.S.standard sieve size). This is primarily for convenience in filling andis not otherwise critical. A small amount of material is shown in placeat the bottom of FIG. 1. Pouring is continued until a level is reachednear the upper ends of the members 1 and 3. The assembly 1, 3, 5 and theinflling 11 are then preferably vibrated to effect greater compaction.Then the plug 7 is inserted and welded in position so as to trap thematerial 11 between the sheath 1, core 3 and end plugs 5 and 7. Theresult is an elemental assembly such as shown in FIG. 2, ready forfurther processing.

As an alternative to pouring the finely divided material 11 into space9, the material 11 can be made into preformed annular pellets orcylinders which can be inserted into space 9 at darts 13. Thereafterplug 7 can be inserted as above.

Further processing comprises a compressive deformation of the containersheath 1 by a reduction in diameter effected by repeated progressiveswaging, wire drawing, extrusion, rolling, tubing or the like, in amanner illustrated in FIG. 3. Assuming that the swaging process isemployed, the usual rotary-head swaging machine may be used, employingby successive passes successive 10% reductions to final size, forexample. Progressive swaging during a given pass is from one size asshown at 15 to another, reduced, size shown at 17 in FIG. 3. Eachsuccessive pass results in a further reduction. A number of passes areemployed until a final very small size in much elongated form is reachedsuch as illustrated in FIG. 4. During the reduction, the particles aresubject to further crushing and packing action with, it is believed,some preferred crystalline orientation occurring with respect to thesleeve axis. Reduction also occurs in the diameter of the core 3, aswell as in the diameter and wall thickness of the sleeve 1. The radialthickness of the mass of material 11 is also reduced.

The reduction is obtained by successive passes for the purpose ofobtaining a solid-phase, interatomic bond between the inner surface ofthe sleeve 1 and the particles lying adjacent thereto; also asolid-phase interatomic bond between the outer surface of the core andthe particles lying adjacent thereto; without the need for subsequentsintering or heat treatment to increase the bond, although suchafter-treatment is not precluded. The stated bonds are lmechanicallyvery strong and, in addition, offer low contact resistance. However,interatomic bonding advantageously does not occur between all of theparticles themselves. The advantage lies in the fact that the statedbreakdown effect is effective between particles and is repeatableinstead of merely catastrophic and nonrepeatable. It is believed thatthis new type of breakdown effect is brought about by ionization of gasalong the margins of the crystallites of the particles of the finelydivided material. This would not occur if they were all interatomicallybonded between themselves, for then the original catastrophic breakdowneffects of the basic crystalline or bulk material would prevail. Statedotherwise, if there were interatomic bonding between all the particles,the breakdown effect, as in the original crystals of the particles,would be catastrophic, whereas without such bonding the breakdown effectoccurs in a repeatable mode, without doing permanent damage.

The criterion for the amount of reduction from the FIG. 2 to the FIG. 4form, in order to obtain a stable product having the desired propertiessuch as the repeatable breakdown effect, is a reduction such as willbring about a resistivity in the compacted particulate mass which is notmore than approximately 200% of the theoretical resistivity; or statedotherwise, a conductivity which is not less than approximately 50% ofthe theoretical conductivity of the material in crystalline or bulkform.

A typical starting dimension for the sheath 1, as illustrated in FIG. 2,may be, for example, l inch outside diameter with a wall thickness ofthe sheath 1 about 1A; inch, with a diameter of the core 3 about 1/3inch, leaving about 1/6 inch for the thickness of the annulus of finelydivided material 11. The given dimensions are primarily such as willprovide in the final pro-duct (sensor) an adequate amount of compressedsolid-state sensing material as an annulus or sleeve of the same,tightly held `between a central core to form one electrical contact, anda surrounding sleeve, ring or band of material to form a secondelectrical contact. For example, the outside diameter of the sheath 1 atthe start of operations may be as high as 2 inches or as small as .090inch. The progressive reduction operation is repeatedly performed untila product of small diameter is obtained (FIG. 4). For example, startingout as stated with an outside diameter of l inch for the sheath 1 (FIG.2), the nal diameter as shown in FIG. 4 may be .020 inch. In thereduction process the length of the assembly shown in FIG. 2' is greatlyextended into coilable wire-like form, as illustrated in FIGS. 4 and 5.As above indicated, the repeated progressive squeezing actions bringabout solid-state interatomic bonds at the interfaces between thecompacted mass of material 9 and the members 1 and 3 but not between allof the crushed particles themselves.

As to the infilling, we have as an example employed finely dividedBa'I'iO3 between a stainless steel sheath of l inch outside diameter anda stainless steel core of about 1/3 inch in diameter (FIG. 2). Inanother case we started with a copper sheath of l inch outside diameterand a copper core 3 of about 1/3 inch in diameter, with an infilling ofA1203. In each of these cases the final outside diameter was .020 inch.We have also started with a copper sheath 1 of .090 inch outsidediameter having a wall thickness of .022 inch and a copper core`diameter of .022 inch, the Whole swaged down to .050 inch. A typicalfinished cross section of an intermediate continuous product P like thatof FIG. 4 is shown very greatly enlarged in FIG. 5. Its concentricity isvery satisfactory.

From the intermediate product of FIG. 4, the final product in the formof the desired sensor is produced by division (shearing, sawing or thelike). A typical resulting form is shown at S in FIG. 6. This comprisesin nal form an outer ring or sleeve providing an outer conductivecontact or terminal 21, an inner core in final form providing an innerconductive contact or terminal 23, and an annular intermediate ring 25which has the characteristics of the improved sensor material. Thelength of the sensor S is determined by the total resistance desired tobe obtained therefrom when connected in an electric circuit through theterminals 21 and 23. The total resistance of the sensor S is a functionof its length as Cut from the intermediate product P. It will beapparent that the product P can be calibrated in terms of resistance perunit of length. Hence sensor resistances are predictable in terms oftheir lengths, which is a convenience in designing apparatus employingthem. Another advantage of the form of the indefinitely longintermediate product of FIG. 4 is that it may readily be coiled forstorage prior to segmentation.

Since the means of fabrication bring about intimate electrical contactunder pressure between the circular terminals 21 and 23 of each sensor Sand the intermediate sensor material 25, there results also extremelygood mechanical and thermal stability of the sensor as a Whole (FIG. 6).An unexpected phenomenon in the case of lanthanum-doped BaTiO3 when usedfor the sensor material 25 is that any original PTC characteristic thatit may originally have had in certain temperature ranges is converted toan NTC characteristic. Other NTC materials in the above list, whichnormally have their NTC properties degraded when in particulate form (aswhen crushed), have these NTC properties reinstrated when subjected tothe swaging operations herein described. This is a great advantagebecause the manufacture by use of particulate materials is much lesstime-consuming and costly than with bulk masses or crystals of the same.

Following is a table showing the percentage change of resistance per C.change in temperature in valid ranges prior to breakdown for sensorsemploying, for example the various filler materials indicated:

TABLE Percent Change of Valid Substances Resistance per Range, C.

C. Change of Temperature Titalsmt'szO 1 6 10 600 a. i 0- sr Tiof. 2. 410o-60o Pb TiOg 1. 6 10G-600 Ceramic (High Temp.):

itesm" t? it a a 0 Ba ZrO 0.4 20D-500 G1 SiC 0.2 10D-700 asses:

g 3. 6 10o-20o Vycor 3. 1 30G-400 2.1 20D-300 Pyrex 2.9 20G-300 1. 550G-600 Lime Glass 9 g-g .5 0-50 Low Temp. Group:

Rochelle Salt 12. 5 25-65 NaNOg (Sodium N itrite) 2g? KNO. (PotassiumNitrate) 25%50 0 00 Sucrose 3. 5 50-150 14. 6 150-200 FIG. 7 is a chartshowing how one -group of materials mentioned in the ta-ble have theirresistivities related to temperature when incorporated in material suchas shown in FIG. 4 or a sensor like the one shown in FIG. 6. This isunder conditions of the application of a 4() v. electric eld. FIG. 8 isa chart showing how quartz and the glasses mentioned in the table havetheir resistivities related to temperature when incorporated in materialsuch as shown in FIG. 4 or a sensor like the one shown in FIG. 6. Thisis under conditions of the application of a 42 v. electric field. Itwill be understood that if the applied voltages indicated in FIGS. 7rand 8 were to -be increased, the curves shown would all shift to theleft and vice versa. As a result, sensors made of material-s havinglbreakdown properties, when used in a suitable circuit to f orm athermostat, may have the breakdown effect occur `at any desiredtemperature (within an appropriate range), said temperature adapted tobe changed by changing the electric field strength (voltage) across theinner :and outer contacts s-uch as 21-and 23 in FIG. 6.

The applied voltages indicated in FIGS. 7 and 8 are arbitrary; Whenother voltages are applied, the breakdown effects will occur at othertemperatures. It will be yappreciated that the breakdown effect whenpresent is a property of the material in its original crystal or bulkform, `but that in such form the breakdown occurs catastrophically,regardless of the temperature at which this occurs. On the other hand,in the compressed particulate form herein described, the temperature atwhich the breakdown occurs again depends upon the voltage applied, but

it becomes repeatable. It Imay also be remarked that advantageously thebreakdown temperature in the compressed particulate form is less thanthe breakdown ternperature in the crystalline form at a given voltage.As a result, catastrophic breakdown at the higher temperature isforeclosed.

FIG. 9 illustrates novel thermostatic control apparatus incorporating asa component in an electrical circuit a sensor S of the presentinvention. This circuit includes a transformer T having a primarywinding TP and la secondary windings TS. Transformer T, and apotentiometer P connected across an A.C. voltage source X, constitute anadjustable electrical potential source for this electrical circuit.Primary winding TP is connected across the movable and one fixed contactof potentiometer P. This circuit further includes a sensor S,series-connected with a current-limiting resistor R across secondarywinding TS, and the coil of a relay RY shunt-connected across sensor S.

A second electrical circuit including normally open contacts K of relayRY is provided for electrically energizing a load L from an electricalpower source L1, L2. Load L may be any electrically energized meansvarying the temperature of a body, the temperature of which is to becontrolled. For example, L could be an electrically controlled furnace,an electrically controlled refrigeration system, or an electrical rnotorthat is to be protected against overheating, etc. The load, or theportion of the load which is to have its temperature sensed, ispositioned in heat-exchange relationship with sensor S as indicated -bythe curved dart D. This relay RY is commonly connected in bothelectrical circuits, receiving its control stimulus from the firstcircuit including sensor S and changing the conductivity of the secondelectrical circuit including load L from a conducting to a nonconductingmode or state in response to a particular change in the resistance -ofsensor S.

Operation is as follows (FIG. 9):

Assuming L to be an electrical motor that is to be protected fromoverheating, and that 125 C. is selected as the maximum permissibletemperature, then a sensor S is employed which has a resistance thatwill change sharply at a temperature in the order of 125 C., e.g., asensor of this invention with compressed particulate sodium nitrite. Themagnitude of the electric field across sensor S is adjusted by varyingthe setting of the movable contact of potentiometer P until theresistance of sensor S sharply decreases at 125 C. from a relativelyhigh value (e.g., in the order of several thousand ohms at sensortem-peratures less than 125 C.) to a relatively low value (e.g., on theorder yof an ohm or less). If the temperature at which the resistance ofS sharply decreases is below 125 C., the electric field is decreased byadjusting the movable contact of potentiometer P to apply a higherpotential across S, and conversely if the trip temperature of S exceeds125 C., then the electric field is increased appropriately.

After initial calibration or adjustment of the temperature at which theresistance of R sharply decreases is accomplished by proper adjustmentof the electric field, the voltage drop across the high resistance of S(at temperatures below 125 C.) energizes the coil of relay R, thusclosing contacts K and energizing the load L from power source L1, L2.The load circuit continues to remain energized until the temperaturesensed by S exceeds 125 C., whereupon the resistance of sensor S sharplydecreases, thereby reducing the voltage applied to the coil of relay Rto a level below its drop-out value. This deactuation of relay R openscontacts K and thus the load circuit is deenergized, preventingoverheating of the motor. The resistance of R serves to limit thecurrent ow through the Isensor S and secondary TS. It will be understoodthat a D.C. electrical potential source may be used (e.g., a battery andpotentiometer) as the equivalent of the A.C. electrical potential sourceshown in this ernbodiment of PIG. 9.

The FIG. 10 embodiment differs from that of FIG. 9 in that the firstelectrical circuit includes a resistance bridge B, a pair of diodes Dand D1 and a capacitor C. A silicon-controlled rectifier SCR is employedin place of relay RY. A sensor S1 of the present invention, having arelatively steep temperature-resistance relationship and which does notexhibit -a sharp change in resistance within the temperature range to besensed, is utilized in place of the sensor S. The adjustable electricalpotential developed across secondary TS is applied across inputterminals I-1 and I-2 of the bridge 3, the legs of which respectivelycomprise resistances R1, R2 and R3, the fourth leg including an optionalreverse current blocking and protective diode D1 serially connected withsensor S1. Bridge output terminal O-1 is connected to cathode electrode2 of silicon-controlled rectifier SCR while output terminal O2 isinterconnected through a rectifying diode D2 to gate electrode 4 of SCR.Capacitor C is shunt-connected across the gate-cathode circuit of SCR.

A second electrical circuit is provided for electrically energizing loadL from the A.C. power source L1, L2. Serially connected in this circuitwith the power source or supply and load L is the power-carrying circuitof rectifier SCR which includes its anode 4, electrode 6 and cathode 2.Thus the SCR is commonly connected in both electrical circuits,receiving its control stimulus from the first circuit including thesensor S and changing the conductivity of the second electrical circuitincluding the load L from a conducting to a nonconducting mode or statein response to a particular change in the resistance of sensor S. Thedotted dart H indicates a heat-exchange relation between L and S1.

Operation is as follows (FIG. 10):

The parameters of R1, R2, R3 and S1 are so selected that when anelectric field with a preselected magnitude (less than the value of thepotential applied -across bridge input terminals I1 and I-2) is appliedacross sensor S, its resistance at a predetermined temperature relativeto the ohmic values of R1, R2 and R3 will provide a D.C. potential(measured -across the gate-cathode circuit of rectifier SCR) which isslightly less than the switching or turn-on potential for the particulartype silicon-controlled rectifier employed. Assume the load L in thisinstance to be lan oven or furnace unit with sensor S in heat exchangewith the space to be heated and the electric heating element,solenoid-actuated gas valve, etc. The load is connected in theanode-cathode circuit of SCR. The bridge will be substantially balancedat the predetermined temperat-ure of the oven. At temperatures below thepredetermined temper-ature the resistance of S1 is relatively greaterand the bridge will be unbalanced as the voltage drop across S1 isgreater than across R1, thereby developing a D.C. potential across thebridge output terminals O-1, O-2, the polarity of the latter beingpositive relative t0 0 1. Thus, the SCR will continue to conduct duringevery half-cycle of the A.C. supply, thereby continuing t-o energizeload L. As the temperature sensed by S1 rises to the predeterminedlevel, the resistance of sensor S1 and thus the voltage drop thereacrossdecreases until the bridge is substantially balanced and the D.C.potential across O-1, 0 2 is insuiiicient to maintain rectifier SCRconducting. As the temperature sensed decreases, the voltage Iacross S1increases as its resistance increases until the gate-cathode signalapplied to it by the bridge again triggers the SCR. Thus, thetemperature of the load L may be maintained substantially constant atthe predetermined temperature. To adjust the predetermined temperatureto another preselected value, the movable contact of potentiometer P issimply moved to increase the electric field applied across sensor S ifthe preselected temperature is to be a higher value, or to decrease theelectric field if a lower trip or preselected control temperature ischosen. Optional diode D1 prevents a reversal of current ow through thebridge including sensor S1 in the event of a temperature overshoot.

It'will be understood that the FIG. 10 apparatus is also useful as athennostatic control if a sensor is employed which has a sharp decreasein resistance in the desired temperature range. In such event, thetemperature at which the sharp resistance decreases occurs is adjustedby variation in the electric field so that the resistance of such sensordecreases at this trip temperature so that the voltage drop across S1 issharply diminished and the SCR gate potential falls below that whichwould trigger it.

In view of the above it will be seen that the invention has severalfeatures which are unique, as follows:

(1) The process of fabrication by comminution or crushing as described.affords a unique means of making sensors having great mechanical andthermal stability, and excellent connections between their sensingcomponents and their terminals, said sensing components in uncrushedforms having heretofore been precluded from practical use.

(2) The means of fabrication using particulate crushed materials affordsa means by which sensor structures can be produced having far greateruniformity of characteristics from point to point than would otherwisebe possible.

several spaced interior tubes such as 59 may be employed.v

The advantage of the invention as illustrated in FIG. 1l is that byusing a number of cores or sheaths an appropriate sensor can performseveral dilferent functions at the same or different times.

In FIG. 12 is shown a form of the invention which is like that shown inFIG. 1, except that there is substituted for the rod or wire core 3 atube. Thus in FIG. 12, numeral 31 indicates the swaged conductive outermember 31, and 71 illustrates the inner tube, with an infilling betweenthe tube 71 and the sleeve 31 of particulate material 73 such as any ofthose above described. This provides one signal channel 75. Theadvantage of this form of the invention is that when the sensor isintroduced into a suitable medium, some of it can be introduced into thetube 71, which increases the heat-transmitting surface, so that thetemperature of the lling 73 responds more quickly to any change intemperature.

(3) The temperature-resistivity characteristics of the sensors beingvariable under a variable applied electric field, makes them extremelyuseful to make thermostatic devices with few or no moving parts, otherthan possibly their comparatively simple control potentiometers, or thelike.

' (4) The process can be utilized (a) to change certain substances, suchas lanthanum-doped BaTiO3, which exhibit PTC characteristics in certainranges and NTC char- Iacte'ristics in other ranges, into completely NTCmaterials, and (b) to more economically prepare any NTC materials foruse as sensor elements.

(5) Any breakdown effect is not catastrophic, so that sensors employingsuch breakdown effects may be operated many times through the breakdowncycle, with no damage or substantial change in characteristics.

(6) The electrical resistivity of the swaged particulate sensingelements assumes closely the characteristics of a single crystalspecimen, even though all the swaged particles are not bondedinteratomically. Thus the magnitude of the resistivity can, further, bevaried substantially during manufacture over a wide range by varying theamount of reduction in the swaging operation.

In FIGS. -l1 and l2 are illustrated structures from which additionaladvantages ow. The method of manufacture of. these forms, theirmaterials and general operation willbe clear from FIGS. 1-10 and theabove de-l scriptions..

In FIG. 11 is shown an arrangement for obtaining different sign-als indiiferent channels. In this form the outer conductive swaged sleeve 31contains an inner conductive swaged sleeve'59 ywith an intermediatecompressed NTC particulate filling numbered 61 of one composition suchas, for example, powdered alumina. Within the inner sleeve 59 is located.a core rod or wire 63. Between it and the conductive sleeve 59 is aninfilling yof a second compressed composition such las powderedzirconium oxide 65. At 67 and 69 are shown different signal channels. Ineach the signal is different upon heating the sensor to its conductivestate, because of the different reversible breakdown resistivities ofthe materials 461 and 65. Moreover, in this case the signals will occurat different temperatures because of the different breakdowntemperatures of the m-aterials 61 and 65.

It will be apparent that the FIG. l1 form of the invention may be madeby inserting the members 59 and 63 into the outer member 31 and theninlling the particulate materials 61 and 65, after which a swagingoperation is performed which is operative upon both members 31 and 59.Or, the core rod 63 may be inserted into the member 59 and the material65 introduced therebetween, after which the member 59 is initiallyswaged so as to com- In view of the above, it will be seen that theseveral objects of the invention are achieved and other advantageousresults attained.

As many changes could be made in the above methods, constructions andproducts without departing from the scope `of the invention, it isintended that all matter -contained in the above description or shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:

1. An electrical temperature sensor comprising a plurality of elongatedelectrically conductive, spaced core members, an elongated outerelectrically conductive tubular member surrounding and spaced from thecore members and essentially axially coextensive therewith, one of thecore members is in the form of a tube and the other is of rod-like formtherein, and compressed particulate material contained, throughout asubstantial portion of the axial length of the members between the coremembers and between them and the outer conductive tubular member, theparticulate material having two portions, the one of which is compressedbetween the tubular members and the other of which is compressed betweenthe inner tubular core member and the rod-like core member therein, thematerial being characterized in that its resistivity decreases withincrease in its temperature and a solid-phase, interatomic bond existingbetween the core members and the adjacent particulate material andbetween the tubular member and the adjacent particulate material.

2. An electrical temperature sensor comprising an electricallyconductive outer tubular member surrounding an electrically conductivetubular core and essentially coextensive therewith along its axiallength, and a mass of particulate NTC material forced into compressionaround the tubular core throughout a substantial portion of the axiallength of the tubular member and core by the outer tubular member and asolid-phase, interatomic bond existing between the tubular member andthe adjacent particulate material and between the tubular core and theadjacent particulate material, the material being characterized in thatit has a repeatable breakdown resistivity.

3. An electrical temperature sensor comprising an electricallyconductive rod-like core, a iirst electrically conductive tubular memberspaced from and surrounding the core and essentially axially coextensivetherewith, a second electrically conductive tubular member spaced fromand surrounding the lfirst: tubular member and essentially axiallycoextensive therewith, a lirst mass of particulate NTC material betweenthe rod-like core and the rst tubular member throughout a substantialportion of the axial length of the rod-like core and the first tubularmember, a second mass of particulate NTC material between the trst andsecond tubular members throughout a substantial portion of the axiallength of the tubular members, the particulate materials being forcedinto compression by at least one of the tubular members, the compressioneffecting conductivities in the respective materials which are not lessthan approximately 50% of the theoretical conductivity of the materialfrom which particles have been formed, the materials being characterizedin that they have repeatable breakdown resistivities and a solid-phase,interatomic bond existing between the rod-like core and the adjacentparticulate material and between the tubular members and the adjacentparticulate material.

4. An electrical temperature sensor comprising an inner tubularelectrically conductive core, an outer electrically conductive tubularmember spaced from and surrounding the core and essentially axiallycoextensive therewith, NTC particulate material between the member andthe core throughout a substantial portion of the axial length of thetubular member and core and a solid-phase, interatomic bond existingbetween the core and the adjacent particulate material and between thetubular member and the adjacent particulate material.

5. An electrical temperature sensor, comprising an electricallyconductive tubular outer electrode member surrounding an electricallyconductive inner electrode tubular core member spaced from the outerelectrode and essentially coextensive therewith along its axial length,a mass of particulate NTC material inlling the space between the tubularmembers throughout a substantial portion of the axial length, theparticulate material being held in compression by the tubular members,and a solid-phase, interatomic bond existing between the tubular membersand the adjacent particulate material, the compression of the masseffecting an electrical conductivity therein which is not less thanapproximately 50% of the theoretical conductivity of the material fromwhich the particles have been formed, the material being characterizedin that it has a repeatable breakdown resistivity at a certaintemperature.

6. An NTC electrical sensor having a voltage-adjustable repeatableresistance-breakdown temperature, comprising a metallic tube forming anouter electrode and a plurality of metallic cores spaced from each otherand from the metallic tube, the cores essentially coextensive with thetube along its axial length, one core of tubular form, another core ofrod-like form and located within the tubular core, the cores formingseveral inner electrodes within the outer electrode whereby severalpairs of electrodes are formed, a rst compacted mass of particleslocated in the space between the outer electrode and the tubular core, asecond compacted mass of particles located in the space between thetubular core and the rodlike core, the material composing the particlesbeing selected from the group consisting of inorganic insulators,inorganic semiconductors, crystalline organic conductors and glass, themasses of particles surrounding the cores throughout a substantialportion of the axial length of the tube, thereby forming severalvoltage-adjustable conductive paths between the electrodes, a numberless than all of the particles in the masses being solid-phaseinteratomically bonded to one another for strength and to provide aresistivity greater than that of the resistivity of an equal solid massof material, particles lying adjacent to the inside of the outerelectrode and the outsides of the inner core electrodes beingsolid-phase interatomically bonded thereto respectively to providesubstantial holding strength between all the electr-odes and the massesof particles.

7. A temperature sensor according to claim 6, wherein the shortestelectrically conductive distances between at least some of several pairsof the electrodes are different from one another.

8. An NTC electrical sensor having a repeatable resistance-breakdowntemperature, comprising a first metallic tube forming an outer electrodeand a second metallic tube within the rst tube and spaced therefromforming an inner electrode or core, the electrodes being essentiallycoextensive along their axial length, a compacted mass of particleslocated in the space between the electrodes, the material composing theparticles being selected from the group consisting of inorganicinsulators, inorganic semiconductors, crystalline organic conductors andglass, the mass of particles surrounding the core throughout asubstantial portion ofthe axial length of the tubes, a number less thanall of the particles in the mass being solidphase interatomically bondedto one another for strength and to provide a resistivity greater thanthat of the resistivity of an equal solid mass of material, particleslying adjacent to the inside ofthe -outer tube and the outsides of theinner electrode being solid-phase interatomically bonded theretorespectively to provide substantial holding strength between theelectrodes and the mass of particles.

9. A sensor according to claim 1 in which the two portions ofparticulate material are composed of different compositions to therebyfacilitate the obtaining of different signals upon heating ofthe sensor.

References Cited UNITED STATES PATENTS 2,782,290 2/ 1957 Lannan et al338-26 2,962,680 11/1960 Sidaris` 338-9 3,017,592 1/1962 Keller et al338-28 3,064,222 ll/ 1962 Renier 338-25 3,068,438 12/1962 Rollins 338-223,089,339 5/1963 Rogers et al. 73-362 3,109,227 ll/ 1963 Goodyear338--10 RICHARD M. WOOD, Primary Examiner.

WILLIAM D, BROOKS, Assistant Examiner.

6. AN NTC ELECTRICAL SENSOR HAVING A VOLTAGE-ADJUSTABLE REPEATABLERESISTANCE-BREAKDOWN TEMPERATURE, COMPRISING A METALLIC TUBE FORMING ANOUTER ELECTRODE AND A PLURALITY OF METALLIC CORES SPACED FROM EACH OTHERAND FROM THE METALLIC TUBE, THE CORES ESSENTIALLY COEXTENSIVE WITH THETUBE ALONG ITS AXIAL LENGTH, ONE CORE OF TUBULAR FORM, ANOTHER CORE OFROD-LIKE FORM AND LOCATED WITHIN THE TUBULAR CORE, THE CORES FORMINGSEVERAL INNER ELECTRODES WITHIN THE OUTER ELECTRODE WHEREBY SEVERALPAIRS OF ELECTRODES ARE FORMED, A FIRST COMPACTED MASS OF PARTICLESLOCATED IN THE SPACE BETWEEN THE OUTER ELECTRODE AND THE TUBULAR CORE, ASECOND COMPACTED MASS OF PARTICLES LOCATED IN THE SPACE BETWEEN THETUBULAR CORE AND THE RODLIKE CORE, THE MATERIAL COMPOSIING THE PARTICLESBEING SELECTED FROM THE GROUP CONSISTING OF INORGANIC INSULATORSINORGANIC SEMICONDUCTORS, CRYSTALLINE ORGANIC CONDUCTORS THE GLASS, THEMASSES OF PARTICLES SURROUNDING THE CORES THROUGHOUT A SUBSTANTIALPORTION OF THE AXIAL LENGTH OF THE TUBE, THEREBY FORMING SEVERALVOLTAGE-ADJUSTABLE CONDUCTIVE PATHS BETWEEN THE ELECTRODES, A NUMBERLESS THAN ALL OF THE PARTICLES IN THE MASSES BEING SOLID-PHASEINTERATOMICALLY BONDED TO ONE ANOTHER FOR STRENGTH AND TO PROVIDE ARESISTIVITY GREATER THAN THAT OF THE RESISTIVITY OF AN EQUAL SOLID MASSOF MATERIAL, PARTICLES LYING ADJACENT TO THE INSIDE OF THE OUTERELECTRODE AND THE OUTSIDES OF THE INNER CORE ELECTRODES BEINGSOLID-PHASE INTERATOMICALLY BONDED THERETO RESPECTIVELY TO PROVIDESUBSTANTIAL HOLDING STRENGTH BETWEEN ALL THE ELECTRODES AND THE MASSESOF PARTICLES.